Electrostatic Sector Fields Research Articles

The 2nd Order Focusing by Energy for TOF Sector Field Mass Analyzer with an Orthogonal Acceleration: Theory, Modeling, Experiment

Currently axially symmetric type of analyzer with an electrostatic sector fields (AESF) is rarely used to construct time-of-flight mass spectrometers. The main drawback, hindering the wider use of the analyzers of this type, is the lack of chromatic second-order focusing by energy. However, the configuration of AESF in combination with orthogonal accelerator (OA) allows to achieved it through compensation of energy aberrations of the analyzer in the system of orthogonal input of the ion beam. In the presented work the results of theoretical calculation, simulation and experimentally obtained data are compared. Characteristics of the analyzer with OA in a large extent depend on the parameters of the incoming ion beam. Data of modeling the 2nd stage of gas-dynamic interface, which have the greatest influence on the parameters of the ion beam, is provided.

Multipass time-of-flight mass spectrometers with high resolving powers

Low energy ions can be stored in “rings” of electrostatic sector fields or in systems of electrostatic mirrors between which the ions are reflected back and forth repeatedly. Because of the long flight path in such systems they very well can be used as precision time-of-flight mass spectrometers. This statement is trivial for monoenergetic ions but also holds for polyenergetic ions if the ion–optical system is designed such that it guides more energetic ions on appropriate detours that cause the overall ion-travel times to become energy independent. Since the number of reflections between the mirrors can be varied by changing the timing of the voltage pulses on the mirrors, either a long well resolved mass spectrum can be recorded or only a section of such a mass spectrum for which then the mass resolving power is increased proportional to the number of reflections.

Time-of-Flight Analysers with Sector Fields: Advances and Prospects

This paper is devoted to the problem of using time-of-flight mass spectrometers with axially-symmetric electrostatic sector fields. The general theory of these analysers takes into account both magnetic and electrostatic fields. Time-of-flight mass analysers with electrostatic fields are considered as a particular case. The conditions of triple focusing are given and formulae for their calculation are presented. Some calculated characteristic data for such analysers demonstrate their capabilities. Results of analyser testing are also presented. A resolution of 1000 is demonstrated; this resolution can be increased up to 10,000 by correction of time aberrations.

Ion energy distributions in SiCl 4 and Ar/O 2 dry etching discharges

Mass-resolved energy distributions (IEDs) are reported for a variety of ions striking the grounded electrodes of two dissimilar dry etching reactors operating at 13.56 MHz. All IEDs are recorded using the same electrostatic sector field energy analyser/quadrupole mass analyser combination. The chemistries studied are the etching of III–V multilayer structures in SiCl 4 plasmas and photoresist removal in Ar/O 2 plasmas. Values for plasma potential are determined and contrasted with theoretical predictions. The predominantly collisionless IEDs show peak splittings in good agreement with an analytical model, from which the dependence on ion mass and sheath width are etermined. A marked decrease in sheath width in O 2 and SiCl 4 plasmas compared with argon is inferred and attributed to the effect of negative ions.

Time- and Space-Focusing Detector System for Real-Time Electron Beam Testing

A new real-time detector system which enables time resolution in the picosecond region is proposed. The system combines the principle of time- and space-focusing actions and the operating principle of the streak tube. Secondary electrons extracted by high voltage are focused in time onto the center of a sweeping deflector and are focused in space onto the screen. Two models are designed in the first-order approximation. One model utilizes an electrostatic toroidal sector field which has simultaneous time- and space-focusing properties. The other model uses a retarding field for time focusing and electrostatic lenses for space focusing. The analyzed results in both models show that the time resolution of about 5 ps can be realized. The collection efficiency of emitted secondary electrons is in the order of 10-2.

Image aberrations of poloidal toroid electrostatic analyzers

The transfer matrix of poloidal electrostatic sector fields is determined by tracing ion trajectories through the calculated potential distribution. To first order this is achieved by numerical ray tracing calculations and to higher order by tracing the expansion coefficients of a paraxial trajectory.

A new AMS facility in Erlangen — status and first results

A new beamline for AMS measurements has been built at the Erlangen EN tandem accelerator. The main components at the low-energy side of the accelerator are a cesium sputter ion source and a 90° injection magnet. At the high-energy side, a 15° electrostatic sector field, a 55° analyzing magnet for the separation of Be and C isotopes, and a gas-filled ionization chamber are used. In 14C test measurements of charcoal, pit-coal and graphite samples, using a preliminary and simple ion source, the 14C events could be clearly separated from the background. The system will be completed with a newly developed high-current ion source, which is presently being installed, and with a 120° mass spectrometer, which will be used for measuring heavier ions such as 26Al, 36Cl, 90Sr and 129I.

Stigmatic sector-field energy analyzer without second-order angular image aberrations

An electrostatic sector field consisting of a toroidal condenser is described which images stigmatically like a spherical condenser but has a larger energy dispersion. Moreover, both the radial and axial image aberrations of second order can be made to vanish simultaneously, which is not possible with a spherical condenser.

A new AMS beam line at the Erlangen tandem accelerator facility

An accelerator mass spectrometry beam line is presently being built up at the EN tandem accelerator in Erlangen. A new Cs sputter ion source is being developed, and mass separators on both the low- and high-energy sides of the tandem and an electrostatic sector field for charge-state selection have been installed. Optimization of the beam quality will be possible with a new emittance measuring device. The tandem is stabilized via a position-sensitive Faraday cup, which simultaneously measures the current of the abundant isotopes. The spectra of the rare-isotope ions are taken by differential energy loss measurements in a gas ionization chamber.

Instrumental developments in organic mass spectrometry

Mass spectrometry is a conglomerate of numerous technical and methodological approaches and recently, new developments in all its fields occur rather frequent. The stimulation has at least two different major sources: on the one hand the requirements in environmental analytical chemistry enforce an increasing sensitivity accompanied by the necessity to construct small, affordable spectrometers. On the other hand, modern biochemistry needs not only sensitivity, but new, compatible inlet techniques to solve the analytical problems in biotechnology, molecular biology and medical sciences. Consequently, small detectors for gas and liquid chromatography with almost inconceivable sensitivity and high performance spectrometers to handle large molecules up to several ten thousand daltons have been developed. New desorption techniques with atom and ion beams or lasers have been designed, several new chromatographic techniques are now compatible with MS, only to name capillary zone electrophoresis, isotachophoresis and even thin layer chromatography. Todays analyzers are small quadrupoles or ion traps, time of flight instruments, ion cyclotrons or arrangement of electrostatic and magnetic sector fields in numerous possible orders and combinations (MS/MS). Very recently, even the detector systems experience a revolution from the electron multipliers to simultaneous detection systems based on array detector devices, which improves the detection capability by orders of magnitude particularly for the analysis of large molecules such as biopolymers.

High-resolution accelerator-based mass spectrometry at isotrace

A method of high-resolution and broad-band Accelerator Mass Spectrometry (AMS) is described using time-of-flight detection through an isochronous arrangement of electrostatic sector fields.

Particle flight times through electrostatic and magnetic sector fields and quadrupoles to second order

The difference between the flight times of a reference particle — moving along the optic axis of some electric or magnetic optical element — and some particle moving along an arbitrary trajectory is calculated. Taken into account are all terms of first and second order in the small quantities χ, α, γ, δ, γ and β. The results are presented in the form of transfer matrices including mass and energy dispersion so as to match magnetic and electrostatic fields.

First order transfer matrices for relativistically fast particles in magnetic and electric sector fields and quadrupoles

The lateral motions and flight time deviations of relativistically fast particles in magnetic or electrostatic sector fields or quadrupoles are described. All effects are presented in the form of transfer matrices.

A Q-value for energy-focused, time-of-flight spectrometers

The flight time through electrostatic and magnetic quadrupole lenses and sector fields is described in the form of transfer matrices for charged particles of different mass and energy. Analogous to the Q Δ-value for angle-focused and lateral-dispersive spectrometers, a Q τ-value is introduced for energy-focused, time-of-flight spectrometers which allows an easy estimate of the quality of such systems.

Focussing errors of a multiple-focussing time-of-flight mass spectrometer with an electrostatic sector field

The second-order focussing errors in time and space of a multiple-focussing time-of-flight mass spectrometer are calculated. Dispersion in time of flight and mass resolution are derived as functions of the relative spread of the initial energy (δ) and of the radial and axial aperture angles (α 0, β 0). The dimensions of the entrance slit ( u 0, v 0) and the original ion pulse length (Δ t i) are additional parameters. For a typical instrument with 157-cm equivalent path length, 500-eV ion energy, δ = ±5%, α o = β o = ± 1.3°, and Δ t i = 65 ns, a resolution of 150 is obtained. For α o = ±1.3°, β o = ±1°, δ = ±2.25% and Δ t i = 10 ns, the resolution increases to 430.

Particle trajectories in a toroidal condenser calculated in a third order approximation

Radial particle trajectories in a toroidal condenser are calculated in a third order approximation and presented in the form of a transfer matrix. Together with the field calculations performed recently the here derived results should make it possible to determine image aberrations of third order for electrostatic sector fields. The potential distribution in the condenser is assumed to come from perfect toroidal electrodes. All formulas are written in a manner that is especially suitable for numerical computer calculations.

New Directional and Energy Focusing Time of Flight Mass Spectrometers for Special Tasks in Vacuum and Surface Physics

This paper describes a variety of new directionally focusing TOFMS with equal momentum or equal energy acceleration and with no first order dependence on ion velocity in time of flight. This is achieved by combining linear drift spaces with magnetic or electrostatic sector fields. Mathematical expressions for velocity focusing are presented together with the requirements for directional focusing, and the characteristic values of a number of geometries which afford stigmatic imaging are given. With special configurations it is further possible to avoid any first order dependence of resolution on slit width. Finally, the resolution is also strongly influenced by the different means of ion production and acceleration. TOFMS with magnetic sector fields and equal momentum acceleration seem well suited for gas analysis together with the coincidence method, while the combination of a sputtering ion source with an electrostatic instrument is particularly promising for the analysis of solids and surfaces.

Image aberrations of second order of electrostatic sector fields

The ion optical properties of electrostatic sector fields are described here in a second order approximation for three dimensional particle trajectories. All influences of the fringing fields are taken into account in the same approximation. The resultant aberrations differ considerably from older expressions as far as they have been calculated. This work is the counterpart to an article on image aberrations of a magnetic sector field 1), in which also a possibility is shown, how such aberrations can be corrected.

Second order transfer matrices of real magnetic and electrostatic sector fields

With the help of second order transfer matrices 1 ) it is easily possible to calculate focusing and dispersion properties as well as second order image aberrations of any ion optical apparatus consisting of one or of several sector fields. Taking into account, in addition to the defrections in the main fields, all effects of the fringing fields 2,3 ), such transfer matrices are presented here for magnetic and electrostatic sector fields which have circular main paths in the main deflecting fields.

Image aberrations of second order for magnetic and electrostatic sector fields including all fringing field effects

As a result of calculations of charged particle trajectories in the main field and in the fringing field of magnetic and electrostatic sector shaped analyzers image aberrations of second order are discussed. Hereby special emphasis is placed upon the influence of the fringing fields.